Posted
by
Soulskillon Friday November 12, 2010 @04:51PM
from the but-does-disney-have-a-trademark dept.

astroengine writes "Look out, the battle of the dwarf planets is about to re-ignite! During last weekend's rare occultation of a star by Eris, astronomers managed to gain one of the most accurate measurements of Eris' physical size. When three Chilean telescopes watched the star blink out of sight, astronomers were shocked to find that Eris is actually a lot smaller than originally thought. So small that it might be smaller than Pluto. On speaking with Discovery News, Eris' discoverer Mike Brown said, 'While everyone is more interested in the "mine is bigger than yours" aspect, the real science is the shockingly large density of Eris.' The mass of Eris is well known, so this means the object is more dense than Pluto. Does this mean the two mini-worlds have different compositions? Did they evolve differently? In light of this finding, is the underlying argument for Pluto being demoted from the planetary club on wobbly ground?"

I remember being so confused about the Pluto controversy. Maybe it's just because I'm not an astronomy nerd but I don't understand the uproar about correcting a miss-classification of a heavenly body... I remember Neil Desgrasse Tyson on the Colbert Report chiming in that it was just a simple fact. Any of you astronomy nerds reading that could explain the emotional reaction? (Not to assume, was it astronomy nerds that were upset? Maybe it was Astrology people that were upset.)

I think that it has a lot to do with the fact that a shockingly large number of people confuse nomenclature with knowledge. Because of that, a fairly fiddly technical discussion over how best to handle astronomical nomenclature hit the popular press as "zOMG pointy-headed scientists don't even know if Pluto is a planet!!!!!"

Naming is not a trivial thing, good nomenclature makes the world a much easier place, crap nomenclature makes it a mess wholly without reason; but either way it seduces people into forgetting that names are simply constructs, assigned for our convenience to bundles of real things. Sometimes, you have to revise the constructs to make the nomenclature better, simpler, more expressive, whatever; but that is very different from changing the bundle of real things and attributes.

The problem is that nobody was taught a planetary mnemonic that included Ceres, Pallas, Juno, and Vesta. As far as people are concerned if it's in the mnemonic, it's a planet. If it's not, then it's not. Their understanding doesn't go any further than that. To them, saying "pluto isn't a planet anymore" is very much like saying "Q isn't a letter anymore".

It's not a misclassification. It's not as if they had a definition of a planet and then suddenly figured out that Pluto didn't fit it--that would be a misclassification. Pluto is no longer classified as a planet because they wrote the definition just now specifically to exclude it.

No it isn't. It's a definition, and an arbitrary one since the class "planet" as currently defined has no particular physical significance. "Member of the list of planets of Sol" is no less (and no more) "factual".

Don't forget the real reason that they wanted to change the definition in the first place: current theory predicts that there are probably hundreds, if not thousands of bodies in the outer solar system with basically the same composition and orbit as pluto, and only slightly smaller. There would be no logical reason to exclude those hundreds of bodies from the list of planets without also excluding Pluto, since there is little qualitative difference between them.

I was just addressing the mentioned "issue" - but yes, exciting times (*) ahead, with many new discoveries almost certainly awaiting. My personal favorite at this point is Sedna, and not only because the timing (relative to its orbit) of the discovery hints at many such bodies - there's also some slight possibility it formed in another star system.

(*)Also because IMHO, if we will ever reach the stars, gradual spreading towards and across our Oort cloud (and eventually, after thousands of years, some groups

(*)Also because IMHO, if we will ever reach the stars, gradual spreading towards and across our Oort cloud (and eventually, after thousands of years, some groups hitching a ride in the clouds of passing star) seems like the way to go (though embryo colonization also looks practical)

The sky calls to us -- and if we do not destroy ourselves, we will, one day, venture to the stars.

actually, that was the reason they wanted a clear definition of 'Planet'. Pluto not being a planet is the results of those discussion, not the cause.

There would be nothing wrong if the definition included Pluto and all those other similar objects.

That may be true but it's naive to think that the motivation for defining "Planet" didn't color the discussion. The original parent is correct in that this was motivated by the perceived inconvenience of having a large number of bodies that would meet the definition.

The whole vote was a sham in my opinion, because there were other reasonable definitions that got suppressed in discussion because of the issue the parent is raising. The current definition is ridiculous and completely context-dependent, fuzzy,

The primary reason for the dwarf planet classification is the sane definition that would have made Pluto and similar bodies planets was based on having sufficient gravity to be spherical. That definition would have expanded the number of planets to a very large number with many of them being bodies in the asteroid belt. Having a planet being defined as a body sufficiently massive to clear its orbit kept the number of "planets" sane and has some practical connection to our current theories and understanding

It's obviously not about complete clearing of the path, but rather of, well, dynamic dominance in his part of space. The planets do that, even if some orbit crossing or near orbit asteroids are left. Pluto and Eris are in a whole crowd of crap and have not in any way achieved a dominant position in that crowd of crap. In the end, it's just nomenclature

Please compare the total mass of all Neptune-crossing bodies to those gravitationally bound to Neptune. You will clearly find that Neptune has cleared the neighborhood. Neptune has a planetary discriminant of 2.4 x 10^4. A body with discriminant >= 1 is considered a planet.

The way the technical definition of clearing the neighborhood is set up, Neptune does.

The real problem is that picking clearing the neighborhood in the first place is completely arbitrary. They could have picked "has an atmosphere" and ended up with Mercury being disqualified as a planet. They could have defined Jupiter as a failed star and disqualified Jupiter as a planet. They could have picked a size limit at Pluto's size and we'd have had 10 planets.

Definitions that are reasonable and include Pluto make the number of things we then have to call planets a rather large number. The current definition has some footing in our understanding of how planets form, which is that bodies like Pluto are essentially the remnants of areas of the solar system that failed to coalesce into planets, namely the Kuiper Belt and Asteroid Belt.

Draw a dot, and eight concentric circles. The circles represent the orbits of the planets. Then draw an oval that touches the outermost circle on one end and goes out 2/3rds further on the other end. That's Pluto.

Below that, draw a straight line corresponding to the width of the circles. Those are the planets viewed edge on. Now draw a straight line tilted 17 degrees. That's Pluto.

And then there are other (non-IAU?) considerations, like:Its not on the same ecliptic plane as the planets.Pluto is not the central mass of its orbital plane. Charon does not directly orbit around Pluto; they both circle around the same point in space (along the orbit around the Sun).Pluto has less mass than many planetary satellites (ex. Moon, Ganymede, Titan, Triton).Pluto has no traits which differentiates it from the asteroids or KBOs.

Pluto is mostly made of various ices (like comets) and travels through the Oort Cloud (like comets). It's orbit is highly eccentric and at a tilt (like comets). Pluto is quite clearly a large comet that never made it to the inner Solar System.
Also, because of it's companion, Charon, the center of gravity for the two is actually between the two. If it were a planet, it would also be unique in this respect as well.

Don't give Eris out yet. There was a lot of discussion on the MPML about this.

First, Eris is definitely more massive, by about 28%. They both have satellites with good orbits, so their masses are pretty well determined.

Second, it is not really that clear that Pluto is really larger than Eris. There have been a number of estimates of Puto's size; by the most recent one presented by Angela Zalucha at the DPS meeting (a radius fit to occultation measurements with a new atmospheric model), Pluto and Eris have roughly the same radius within the respective error bars (1146 +-20 km in diameter for Pluto versus 1170 km for Eris).

What is more interesting to me is that Eris is dense and very bright - could something as rare as Deuterium snow be covering its surface ?

So how long will it take to get there, how big of a dish will it take to get a signal back, and how much plutonium to power the instrument package and radio to find out what is really going on out there?

The argument was as arbitrary as any others. It was basicly "which property is common to both Pluto and Eris, but not found in the other objects traditionally considered planets?".

Pluto always was a weird object to be called a planet, with his density somewhere in the nowhere between the earthlike planets and the gas giants, and being pretty similar to the large moons of the gas giants.

But only when Eris was found, there was a second objekt thought to be similar enough to Pluto to define a new class of "plutolike objects", which allowed Pluto to be demoted from planet status.

So yes, the classification of Pluto in the class of "plutolike objects" (pardon, "Dwarf planets") seems to be on pretty firm ground, considering there are now more objects known in that class (Makemake for instance), though Eris now seems to be a weirdo within this class.

I wasn't arguing how arbitrary it was. I was arguing that the people who created the definition were smart enough to define it in such a way that the classification can be determined on a case-by-case basis. A basis that won't be substantively changed by comparative measurements. Discovering anything about any new planetary body will not change Pluto's classification because the discoveries will not be about Pluto.

I wasn't arguing how arbitrary it was. I was arguing that the people who created the definition were smart enough to define it in such a way that the classification can be determined on a case-by-case basis. A basis that won't be substantively changed by comparative measurements. Discovering anything about any new planetary body will not change Pluto's classification because the discoveries will not be about Pluto.

Here's the definition: "The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune." The rest of the definition is noise because they failed to define "clearing the neighborhood".

The rest of the definition is noise because they failed to define "clearing the neighborhood".

Noise?!

There's FIVE ORDERS OF MAGNITUDE difference in planetary discriminant [wikipedia.org] (mass ratio between the body and all other masses in that orbit) between the highest value for a dwarf planet (Ceres) and the lowest value for a planet (Neptune).

When the difference is a factor of 10,000, there's absolutely no need to create a precise definition, and it would be foolish to do so.

It's like you're arguing that the definition of what is or isn't ocean is useless because it doesn't precisely define at what point of the tide cycle, or how far up a river mouth, it transitions from ocean to not ocean. But the question we're asking is whether Topeka, Kansas is in the ocean or not and the answer is obviously NO!

You might as well argue that it's completely arbitrary to say that you are alive and Benjamin Franklin is dead, because science has not precisely defined the exact line between dead and not dead. Um, I think it's still pretty clear which is which in this case.

You see, if they did actually define "clearing the neighborhood" in a precise manner, that would be the truly arbitrary choice. But when you look at the bodies in our solar system, and you see that there's a small set of objects which outweigh everything else in their orbits by at least a thousand-to-1, and then a great many objects which weigh less than the rest of the objects in their orbit, then yes that actually makes a clear dividing line. You don't have to draw it with infinite precision to see that it's there.

The definiton of Pluto as a planet is far more "noise" than the definition that it isn't. We only called it a planet because we didn't know it was so different from the other ones. It's like when we first discovered Ceres. Only we changed that one pretty quick, even though it's more planet-like than Pluto is.

When the difference is a factor of 10,000, there's absolutely no need to create a precise definition, and it would be foolish to do so.

Well if the IAU was going for an IMPRECISE definition they couldn't have done better. Science is all about definitions. Precision is important. The current definition is an utter mess. I couldn't care less that Pluto was named after a Disney character. If we want to be precise it belongs in a different category BUT

1) They created pair of definitions where a "dwarf planet" is not a "planet. That is confusing and ridiculous.

2) They mention "the sun" and therefore the definition as written excludes extrasolar planets. So now we have "dwarf planets" that are not planets and "extrasolar planets" that techincally also are not planets.

3) The clearing the path part of the definition is an arbitrary requirement and a kludge. It is possible we will discover extrasolar planets that cross each other's orbits in a stable way. Fortunately extrasolar planets aren't planets anyway.

There are other things wrong with the definition, but lets just leave it at that shall we? The definition is beauracratic and in terms of science it is PURE JUNK. Science is about understanding things. We humans do this by classifying them, so definitions are important. However in this case everyone was more focused on whether or not Pluto is a planet and was bending the definition to fit their preference.

Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

What does being geeky have to do with being old and too set in your ways to listen to reason?

Give us an argument why the IAU's definitions of a planet and of a dwarf planet are unreasonable. Please avoid any Appeal to Tradition. Also, can you craft a definition of a planet that covers Pluto but not Eris and Ceres other than "just what we used to arbitrarily call a planet?"

I fear you fail to understand the reason behind the "demotion." What we call it has never made any real difference in what Pluto does or does not do. The only use of these names is to help us understand them better. As such, the terrestrial planets share much in common, the gas giants share much in common, and Pluto shares little with either group. Thus, if you're saying that all Pluto-like objects should be called "planets", it would make some sense except that there are lots of them. If you're saying that Pluto alone should be a planet while similar objects are not, then that's a far less defensible position.

I fear you fail to understand the reason behind the "demotion." What we call it has never made any real difference in what Pluto does or does not do. The only use of these names is to help us understand them better. As such, the terrestrial planets share much in common, the gas giants share much in common, and Pluto shares little with either group. Thus, if you're saying that all Pluto-like objects should be called "planets", it would make some sense except that there are lots of them. If you're saying that Pluto alone should be a planet while similar objects are not, then that's a far less defensible position.

It makes sense, even if there are hundreds of Pluto-like dwarf planets. Let's point out the problems once again:

1) The IAU definition doesn't cover extrasolar planets. Hence, the definition is applicable to only one star system.

2) The IAU definition depends on the dynamics of the system, which can change. This is a weak quibble, but it is feasible on the time scale of millions of years for humanity to deliberately move planets and moons around. Even if nothing else happens, the Moon will become a plan

1) The IAU definition doesn't cover extrasolar planets. Hence, the definition is applicable to only one star system.

Which is actually pretty smart. There are solar systems that we know are wildly different from ours (hot jupiters, massive apparently rocky planets). We don't really have a clue what kind of a universal definition of a planet would make sense and be a useful classification tool.

Better to refrain from making a universal definition of planet, until we have a lot more data points, having observed complete planetary systems around other stars. And that won't happen until we have either interstellar probes or so

How about that the IAU definition excludes "extrasolar planets" from being planets, on account of them not orbiting the sun.

Technically, the IAU definition only covers the distinction between bodies in our solar system and says absolutely nothing about bodies outside of it. This is because there is currently no way for us to determine whether or not any extrasolar planet clears its neighborhood (though we can probably guess for most of the Jupiter-sized ones).

It doesn't say that these bodies aren't planets. If just says that when defining bodies within our Solar System, "planets," "dwarf planets," and "small Solar system bodie

My definition for a planet would be "big enough that scientifically interesting things happen on it that only happen on big objects".

So if it's got an atmosphere, different types of surface, weather, tectonic activity, etc. it's more planetlike. It's a sliding scale rather than a yes or no idea, and you'll probably need to come up with some size threshhold that roughly approximates this (since it's hard to tell if some newly discovered object, that you don't know anything about yet, has anything interestin

Fine, but just be aware that if tradition means nothing there could well be a redefinition of, say, moon. Since the barycentre of our Moon and Earth is (just) beneath the surface of the Earth, we're probably safe for now, but it wouldn't take much of a change in definitions to re-classify Earth-Luna as a double-planet system. Making the Moon, well, no longer a moon.

(not that I think Pluto should be re-instated as a planet - I realise it was only ever just America's "Look, we can discover planets too")

Science progress, and you geezers* can stuff yourselves. For the record, I'm probably older then you. You can gave geeky, I'll stick with nerdy, because I actually know shit.

I'm sure there where people like you when the Greeks figured out the world was round, and there were people like you when the write brothers flew, and there where people like you when phones went cordless, and there will be people like you when we send people to actually walk on Pluto.

Science progresses, and you geezers* can stuff yourselves. For the record, I'm probably older than you. You can have geeky, I'll stick with nerdy, because I actually know jack shit.

I'm sure there were people like you when the Greeks figured out the world was round, and there were people like you when the Wright brothers flew, and there were people like you when phones went cordless, and there will be people like you when we send people to actually walk on Pluto.

At the end of the day, the whole "planet/not a planet" distinction isn't even particularly illuminating. It's much more useful, IMHO, to just look at the parameters and make up your own mind. How massive is it? What's its distance from the sun? What's its eccentricity? What's its inclination (please, no jokes about Uranus' inclination...)? What's its origin?

A binary planet/not planet distinction just doesn't tell you that much.

>Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

And ask anyone my grandmother's age and they'll tell you that they're not really convinced Pluto is a planet because when they were in school in the 1920's, it wasn't a planet, it was just a chunk of rock that nobody had ever seen.

It's perfectly simple: Pluto is not a Dwarf Planet, Pluto is a Fucking Planet. Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

And you'll be as wrong as those who resisted reclassifying Ceres from planet to non-planet.

Oh, what's that, you don't think Ceres is a planet? It's pretty obvious that what just happens to be the biggest asteroid in a giant asteroid belt that's total mass is 3 times this one body is cool, but not

There is this thing called a MAGNIFYING LENS (usually used as a collective system of same) which makes a distant object's apparent size large enough to measure its arc. Put a big enough one of those in orbit and your three qualifications are easily met. The one you don't mention - cost - might be a little problem.

So, in other words, the question is not which one is bigger - Eris or Pluto, but which one is denser - Eris or the astronomers?

Why the insults? Why are people so emotionally attached to the old order in which the term "planet" didn't have a solid, scientific definition which included Pluto (but in which kids didn't learn about similar bodies like Ceres) that they are willing to lash out at astronomers for attempting to put some kind of reason and order into the system?

I honestly can't think of any better demonstration of why humans should never achieve immortality. Look at how attached people are as minor of a belief that they we

A planet in Earth's solar system beyond the orbit of Pluto. Rupert was named Persephone, but nicknamed Rupert after "some astronomer's parrot." It was eventually settled by the Grebulons.In 2005, an actual tenth planet fitting Rupert's description was discovered beyond Pluto (which was considered a planet then, as opposed to a dwarf planet now). In a poll of the public conducted by New Scientist magazine to search out potential names for the object, "Rupert" ranked #5, and "Persephone" was the top ch

Actually, it's the general public that decides the definition of planet, not the IAU. The general public wins because they have the most votes and weapons if it comes down to either democracy or war over it. So get used to it: Pluto is a planet.